Process to remove product alcohol from a fermentation by vaporization under vacuum

ABSTRACT

A fermentation liquid feed including water and a product alcohol and optionally CO 2  is at least partially vaporized such that a vapor stream is produced. The vapor stream is contacted with an absorption liquid under suitable conditions wherein an amount of the product alcohol is absorbed. The portion of the vapor stream that is absorbed can include an amount of each of the water, the product alcohol and optionally the CO 2 . The temperature at the onset of the absorption of the vapor stream into the absorption liquid can be greater than the temperature at the onset of condensation of the vapor stream in the absence of the absorption liquid. The product alcohol can be separated from the absorption liquid whereby the absorption liquid is regenerated. The absorption liquid can include a water soluble organic molecule such as an amine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/427,896, filed Dec. 29, 2010, and U.S. Provisional Application No.61/302,695, filed Feb. 9, 2010, the entire disclosures of which areincorporated in their entirety herein by reference thereto.

FIELD OF THE INVENTION

The present invention relates to processes to remove butanol and otherC₂ to C₈ alcohols from a fermentation broth employing vacuumvaporization.

BACKGROUND

Currently, much industrial fermentation involves the manufacture ofethanol for either chemical or fuels use. For use in fuel, butanol hasadvantages as compared to ethanol, namely butanol has a lower vaporpressure and decreased solubility in water.

An advantageous butanol fermentation process would encompass a complete,or substantially complete, conversion of sugars to butanol withoutreaching a butanol titer above a threshold of butanol tolerance thatcauses the rate of butanol production to fall below an undesirablepredetermined rate. While it may be possible to limit sugar loadings toa level whereby batch fermentation does not require operation at abutanol concentration above the tolerance level, this approach hasdisadvantages because limited sugar loadings result in dilute solutionsthat are themselves economically undesirable to process. Therefore,there is a need for a process by which levels of butanol are limited ina fermentation at or below the tolerance level whilst sugar loadings arenot limited by considerations of the tolerance level.

One means by which a butanol producing fermentation process might bemade more efficient would be to remove the butanol as it is being formedfrom the fermentation medium (broth), so that the tolerance level of thebutanol producing micro-organism is not reached, allowing high loadingof sugar to be charged to the fermentation vessel. Such an “in situproduct removal” or “ISPR” process is described in PCT InternationalPublication No. WO2009/079362 A2.

ISPR processes for fermentation products are also described in theRoffler dissertation (Roffler, Steve Ronald, “Extractivefermentation—lactic acid and acetone/butanol production,” Department ofChemical Engineering at the University of California at Berkeley, 1986).Roffler describes a process whereby a liquid stream from a fermentationvessel is passed to a separate vessel which is held under vacuum.However, the method described in Roffler necessitates further processingof the resulting vapor stream. Because an industrial fermentation relieson microorganisms, such processing must consider temperature constraintsrelative to the microorganisms.

To operate at acceptable temperatures, consideration must be given tocosts and practicalities of cooling or operation under vacuum. The costsassociated with removal of heat within a chemical process can be afunction of the plant location and also the time of the year. In manygeographic areas, it is not possible to guarantee cooling to beavailable or practical at the temperature at which heat needs to beremoved from the vapor stream.

Providing chilled water to the heat exchanger by which condensation iscarried out significantly increases the cost of the cooling medium. Analternative would be to compress the vapor stream to a higher pressureto allow the condensation to be done against cooling water year round,but this too entails significant cost because of the low density of theinitial vapor passing to the machine. Processes described which uselithium bromide for absorption of ethanol and water vapors may not beadequate for absorbing carbon dioxide or higher alcohols of a vaporstream.

In addition, with whatever method is used, there will be a residual gasstream (due to the _(s)olubility of CO₂ in the fermentation broth) thatmust be compressed before discharge to the atmosphere. The residual gasstream will comprise CO₂. While vacuum flashing represents an effectivemeans by which butanol can be removed from a fermentation process, thereis a need for advances in the processing of the resulting low pressurevapor stream containing the product.

SUMMARY OF THE INVENTION

Methods of removing product alcohol from a fermentation by vaporizationunder vacuum are presented. For example, in some embodiments, afermentation liquid feed comprising water and a product alcohol andoptionally CO₂ is at least partially vaporized such that a vapor streamis produced. Methods of recovering a product alcohol from the vaporizedfermentation feed are also presented. For example, in some embodiments,the vapor stream containing the product alcohol is contacted with anabsorption liquid under suitable conditions wherein an amount of theproduct alcohol is absorbed. Also presented are methods of recovering aproduct alcohol from the absorption liquid whereby the absorption liquidis regenerated.

In embodiments, a method includes at least partially vaporizing afermentation liquid feed wherein a vapor stream is produced, thefermentation liquid feed and the vapor stream each including an amountwater, a product alcohol and optionally CO₂; and contacting the vaporstream with an absorption liquid under vacuum conditions wherein atleast a portion of the vapor stream is absorbed into the absorptionliquid to form an absorption liquid phase. The portion of the vaporstream that is absorbed can include an amount of each of the water, theproduct alcohol and optionally the CO₂. The temperature at the onset ofthe absorption of the vapor stream into the absorption liquid can begreater than the temperature at the onset of condensation of the vaporstream in the absence of the absorption liquid.

In embodiments, partially vaporizing the fermentation liquid can includeremoving the fermentation liquid feed from a fermentation vessel;supplying the fermentation liquid feed to a multi-stage distillationcolumn at a suitable flow rate; distilling the fermentation liquid feedto produce the vapor stream enriched in the product alcohol and abottoms stream depleted in the product alcohol, wherein the distillingoccurs under a pressure sufficiently below atmospheric to allow for thevapor stream to be produced at a temperature no greater than about 45°C.; and optionally, returning any portion of the bottoms stream to thefermentation vessel. In some embodiments, the concentration of theproduct alcohol in the bottoms stream is not more than 90% of theconcentration of the product alcohol in the fermentation liquid feed.

In some embodiments, a titer of product alcohol in a fermentation vesselcan be maintained below a preselected threshold pursuant to methodspresented herein. For example, a method can include removing from afermentation vessel a fermentation liquid feed stream comprising productalcohol, water, and optionally CO₂; supplying the fermentation liquidfeed stream to a single stage flash tank or a multi-stage distillationcolumn; vaporizing under vacuum conditions the fermentation liquid feedstream in the single stage flash tank or the multi-stage distillationcolumn to produce a vapor stream enriched in product alcohol and abottoms stream depleted in product alcohol; and optionally returning anyportion of the bottoms stream to the fermentation vessel. In someembodiments, the vapor stream is contacted with an absorption liquidunder vacuum conditions wherein at least a portion of the vapor streamis absorbed into the absorption liquid.

In some embodiments of the methods presented herein, the fermentationliquid feed includes CO₂. In some embodiments, the product alcohol isbutanol. In some embodiments, the absorption liquid comprises a watersoluble organic molecule different from the product alcohol. In someembodiments, the organic molecule is an amine such as monoethanolamine(MEA), 2-amino 2-methyl propanol (AMP), methyldiethanolamine (MDEA), ora mixture thereof. In embodiments, the absorption liquid phase includesa water soluble organic molecule with a boiling point at least 30° C.greater than the boiling point of water. In embodiments, the absorptionliquid comprises potassium carbonate and ethylene glycol. Inembodiments, the absorption liquid comprises ethylene glycol.

In some embodiments, a substantial portion of the CO₂ and at least aportion of the product alcohol or water or both are absorbed intoabsorption liquid.

Also provided herein is a method of recovering a product alcohol from anabsorption liquid phase and regenerating the absorption liquid phase.Recovering the product alcohol may include pumping from an absorber anabsorption liquid phase including an absorption liquid, water, productalcohol, and optionally CO₂, to a higher pressure than a pressure in theabsorber; optionally, heating the absorption liquid phase; feeding theabsorption liquid phase to a multi-stage distillation column comprisinga stripping section and optionally a rectification section; operatingthe distillation column under conditions such that a bottoms productcomprising the absorption liquid and a vapor phase comprising a mixtureof water, product alcohol, and optionally CO₂ are produced; recoveringthe bottoms product comprising the absorption liquid phase from thedistillation column; and recovering the water, the product alcohol andoptionally CO₂ from the vapor phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 illustrates an example system useful for practicing processesaccording to embodiments described herein.

FIG. 2 is a schematic of the static cell PtX apparatus as described inExample 1.

FIG. 3 is a graph of the peak height vs. CO₂ absorbed spectra for amonoethanolamine solution as described in Example 6.

FIG. 4 is a graph of CO₂ absorbed vs. peak height as described inExample 6.

FIG. 5 is a graph of temperature vs. peak height as described in Example6.

FIG. 6A is an example flow diagram for an embodiment of the processesprovided and is referenced in Example 7.

FIGS. 6B and 6C illustrate Tables 8A and 8B, respectively, whichsummarize simulation model results of Example 7.

FIG. 7A is an example flow diagram for an embodiment of the processesprovided and is referenced in Example 8.

FIGS. 7B and 7C illustrate Tables 10A and 10B, respectively, whichsummarize simulation model results of Example 8.

FIG. 8A is an example flow diagram for an embodiment of the processesprovided and is referenced in Example 9.

FIGS. 8B and 8C illustrate Tables 12A and 12B, respectively, whichsummarize simulation model results of Example 9.

FIG. 9 illustrates an example system useful for practicing processesaccording to embodiments described herein.

FIGS. 10A, 10B and 10C illustrate an example system useful forpracticing processes according to embodiments described herein, andspecifically for demonstrating air stripping before vacuum flash.

DETAILED DESCRIPTION

The processes provided herein can be more fully understood from thefollowing detailed description and accompanying figures which form apart of this application. Reference made to figures is intended to aidin the understanding of the processes described herein, and should notbe construed as limiting. In addition, where process conditions areproposed in reference to a figure, these are supplied as an example andvariation from these conditions is within the spirit of the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. In case of conflict, thepresent application including the definitions will control. Also, unlessotherwise required by context, singular terms shall include pluralitiesand plural terms shall include the singular. All publications, patentsand other references mentioned herein are incorporated by reference intheir entireties for all purposes.

In order to further define this invention, the following terms anddefinitions are herein provided.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” “contains” or “containing,” or any othervariation thereof, will be understood to imply the inclusion of a statedinteger or group of integers but not the exclusion of any other integeror group of integers. For example, a composition, a mixture, a process,a method, an article, or an apparatus that comprises a list of elementsis not necessarily limited to only those elements but can include otherelements not expressly listed or inherent to such composition, mixture,process, method, article, or apparatus. Further, unless expressly statedto the contrary, “or” refers to an inclusive or and not to an exclusiveor. For example, a condition A or B is satisfied by any one of thefollowing: A is true (or present) and B is false (or not present), A isfalse (or not present) and B is true (or present), and both A and B aretrue (or present).

As used herein, the term “consists of,” or variations such as “consistof” or “consisting of,” as used throughout the specification and claims,indicate the inclusion of any recited integer or group of integers, butthat no additional integer or group of integers may be added to thespecified method, structure, or composition.

As used herein, the term “consists essentially of,” or variations suchas “consist essentially of” or “consisting essentially of,” as usedthroughout the specification and claims, indicate the inclusion of anyrecited integer or group of integers, and the optional inclusion of anyrecited integer or group of integers that do not materially change thebasic or novel properties of the specified method, structure orcomposition.

Also, the indefinite articles “a” and “an” preceding an element orcomponent of the invention are intended to be nonrestrictive regardingthe number of instances, i.e., occurrences of the element or component.Therefore “a” or “an” should be read to include one or at least one, andthe singular word form of the element or component also includes theplural unless the number is obviously meant to be singular.

The term “invention” or “present invention” as used herein is anon-limiting term and is not intended to refer to any single embodimentof the particular invention but encompasses all possible embodiments asdescribed in the application.

As used herein, the term “about” modifying the quantity of an ingredientor reactant of the invention employed refers to variation in thenumerical quantity that can occur, for example, through typicalmeasuring and liquid handling procedures used for making concentrates orsolutions in the real world; through inadvertent error in theseprocedures; through differences in the manufacture, source, or purity ofthe ingredients employed to make the compositions or to carry out themethods; and the like. The term “about” also encompasses amounts thatdiffer due to different equilibrium conditions for a compositionresulting from a particular initial mixture. Whether or not modified bythe term “about”, the claims include equivalents to the quantities. Inone embodiment, the term “about” means within 10% of the reportednumerical value, alternatively within 5% of the reported numericalvalue.

“Biomass” as used herein refers to a natural product comprisinghydrolysable polysaccharides that provide fermentable sugars, includingany sugars and starch derived from natural resources such as corn, sugarcane, wheat, cellulosic or lignocellulosic material and materialscomprising cellulose, hemicellulose, lignin, starch, oligosaccharides,disaccharides and/or monosaccharides, and mixtures thereof. Biomass mayalso comprise additional components, such as protein and/or lipids.Biomass may be derived from a single source, or biomass can comprise amixture derived from more than one source; for example, biomass maycomprise a mixture of corn cobs and corn stover, or a mixture of grassand leaves. Biomass includes, but is not limited to, bioenergy crops,agricultural residues, municipal solid waste, industrial solid waste,sludge from paper manufacture, yard waste, wood and forestry waste.Examples of biomass include, but are not limited to, corn grain, corncobs, crop residues such as corn husks, corn stover, grasses, wheat,rye, wheat straw, barley, barley straw, hay, rice straw, switchgrass,waste paper, sugar cane bagasse, sorghum, soy, components obtained frommilling of grains, trees, branches, roots, leaves, wood chips, sawdust,shrubs and bushes, vegetables, fruits, flowers, animal manure, andmixtures thereof. For example, mash or juice or molasses or hydrolysatemay be formed from biomass by any processing known in the art forprocessing the biomass for purposes of fermentation, such as by milling,treating and/or liquefying and comprises fermentable sugar and maycomprise an amount of water. For example, cellulosic and/orlignocellulosic biomass may be processed to obtain a hydrolysatecontaining fermentable sugars by any method known to one skilled in theart. Particularly useful is a low ammonia pretreatment as disclosed USPatent Application Publication US20070031918A1, which is hereinincorporated by reference. Enzymatic saccharification of cellulosicand/or lignocellulosic biomass typically makes use of an enzymeconsortium for breaking down cellulose and hemicellulose to produce ahydrolysate containing sugars including glucose, xylose, and arabinose.(Saccharification enzymes suitable for cellulosic and/or lignocellulosicbiomass are reviewed in Lynd, L. R., et al. (Microbiol. Mol. Biol. Rev.,66:506-577, 2002).

The term “vacuum flash” or “flash” refers to a process step whereby aliquid stream from a fermentation vessel is passed to a separate vessel(which can be a multi-stage distillation column or a single-stage tank)which is held under vacuum. The reduction in pressure causes a fraction,typically no more than 10%, of the liquid stream to flash into the vaporphase. A liquid stream subjected to this step may be referred to as“flashed” or “partially vaporized” or “vaporized”. In embodiments wherethe “flash” is carried out in a multi-stage distillation column, theflash may also be referred to as a “distillation” or a “flashdistillation.”

The term “vacuum flash vessel” refers to the physical location in whichat least a fraction of the liquid stream from the fermentation vesselflashes into the vapor phase.

The term “absorption liquid” as used herein refers to a liquidintroduced into the process which is capable of absorbing any portion ofthe vapor phase produced during the flash.

The term “fermentation” as used herein refers to a process step wherebya carbon substrate is converted into a product, such as a productalcohol, by the action of microorganisms.

The term “fermentation broth” or “fermentation liquid” as used hereinrefers to the mixture of water, sugars, dissolved solids, microorganismsproducing alcohol, product alcohol and all other constituents of thematerial held in the fermentation vessel in which product alcohol isbeing made by the reaction of sugars to alcohol, water and carbondioxide (CO₂) by the microorganisms present. From time to time, as usedherein the term “fermentation medium” and “fermented mixture” can beused synonymously with “fermentation broth”.

“Fermentable carbon source” as used herein means a carbon source capableof being metabolized by the microorganisms disclosed herein for theproduction of fermentative alcohol. Suitable fermentable carbon sourcesinclude, but are not limited to, monosaccharides, such as glucose orfructose; disaccharides, such as lactose or sucrose; oligosaccharides;polysaccharides, such as starch or cellulose; carbon substrates; andmixtures thereof. From time to time, as used herein the term“fermentable carbon source” can be used synonymously with “carbonsubstrate” or “fermentable carbon substrate”. The carbon source includescarbon-derived from biomass.

“Feedstock” as used herein means a feed in a fermentation process, thefeed containing a fermentable carbon source with or without undissolvedsolids, and where applicable, the feed containing the fermentable carbonsource before or after the fermentable carbon source has been liberatedfrom starch or obtained from the break down of complex sugars by furtherprocessing, such as by liquefaction, saccharification, or other process.Feedstock includes or is derived from a biomass. Suitable feedstockinclude, but are not limited to, rye, wheat, corn, cane and mixturesthereof.

“Sugar” as used herein refers to oligosaccharides, disaccharides and/ormonosaccharides.

“Fermentable sugar” as used herein refers to sugar capable of beingmetabolized by the microorganisms disclosed herein for the production offermentative alcohol.

The term “product alcohol” as used herein refers to a lower alkanealcohol, such as a C₂-C₈ alcohol produced as a primary product by amicroorganism in a fermentation process.

“Butanol” as used herein refers to the butanol isomers 1-butanol(1-BuOH), 2-butanol (2-BuOH) and/or isobutanol (iBuOH or i-BuOH orI-BUOH), either individually or as mixtures thereof.

The term “recombinant microorganism” as used herein refers to amicroorganism that has been engineered using molecular biologicaltechniques. The microorganism can be optionally engineered to express ametabolic pathway, and/or the microorganism can be optionally engineeredto reduce or eliminate undesired products and/or increase the efficiencyof the desired metabolite.

“Substantial portion” as used herein with reference to a process streamor a component thereof, refers to at least about 50% of the indicatedprocess stream or indicated component thereof. In embodiments, asubstantial portion may comprise about at least about 60%, at leastabout 70%, at least about 80%, at least about 90%, or at least about 95%or the indicated process stream or indicated component thereof.

“Any portion” as used herein with reference to a process stream refersto any fractional part of the stream which retains the composition ofthe stream, including the entire stream, as well as any component orcomponents of the stream, including all components of the stream.

Provided herein are methods by which a fermentation liquid streamleaving a fermentation vessel is processed using a vacuum flash. Thevacuum flash can be carried out in a single stage flash tank.Alternatively or in conjunction, the vacuum flash can be carried out ina multi-stage distillation column under conditions such that a flashedfermentation broth forms a vapor stream enriched in product alcohol anda bottoms stream substantially depleted in product alcohol are produced.As disclosed herein, the vapor stream from the flashed fermentationbroth can be absorbed into a second liquid stream at a highertemperature than it could be condensed on its own. Such processes areuseful for fermentations which produce product alcohols, and, inparticular butanol, because of the desire to remove butanol duringfermentation to diminish impact on productivity and/or viability of themicroorganisms in the fermentation. Processes are therefore providedwhich provide for effective product recovery during fermentation withminimized impact on the optimal fermentation conditions.

During a product alcohol fermentation, the product alcohol is producedin a fermentation liquid by a microorganism from a carbon substrate. Inembodiments, the carbon substrate is provided in a mash derived from aplant source. The fermentation can be carried out under conditions knownto those of skill in the art to be appropriate for the microorganism. Inembodiments, the fermentation is carried out at temperatures of fromabout 25° C. to about 40° C. In embodiments, the fermentation is carriedout at temperatures of from about 28° C. to about 35° C. and inembodiments, from about 30° C. to about 32° C. The fermentation liquidcomprises water and a product alcohol, and typically, CO₂. To recoverthe product alcohol from the liquid using the methods provided herein,at least a portion of the fermentation liquid is removed from thefermentation vessel to a second vessel or “vaporization vessel” and isat least partially vaporized by vacuum flash. For example, in suchembodiments, the vaporization can take place at temperatures of fromabout 25 to about 60° C. under vacuum. The vaporization can take placeat pressures from about 0.02 to about 0.2 bar. It will be appreciatedthat the pressure can be 0.02, 0.03, 0.04, 0.05, 0.1, 0.15 or 0.2 bar,or less than about 0.2 bar. In embodiments, the vaporization can takeplace at pressures of from about 0.05 to about 0.2 bar. In embodiments,the vaporization can take place at a pressure of less than about 0.2bar, or less than about 0.1 bar. Alternatively, the vacuum flash can becarried out in a multi-stage distillation column as described elsewhereherein under conditions described herein.

It is desirable for the vaporization to be initiated and carried outduring the fermentation process such that product alcohol is removed atabout the same rate at which it is produced. It will be appreciated thatthe vaporization will be carried out at a rate and under conditions suchthat the product alcohol in the fermentation vessel is maintained belowa preselected threshold. The preselected threshold will depend on thetolerance of the microorganism to the product. In embodiments, themicroorganism is bacteria, cyanobacteria, filamentous fungi, or yeasts.In some embodiments, the bacteria are selected from the group consistingof Zymomonas, Escherichia, Salmonella, Rhodococcus, Pseudomonas,Bacillus, Lactobacillus, Enterococcus, Pediococcus, Alcaligenes,Klebsiella, Paenibacillus, Arthrobacter, Corynebacterium, andBrevibacterium. In some embodiments the yeast is selected from the groupconsisting of Pichia, Candida, Hansenula, Kluyveromyces, Issatchenkia,and Saccharomyces. In embodiments, the threshold is less than about 20g/L. In embodiments, the threshold is below about 8 g/L, below about 10g/L, below about 15 g/L, below about 25 g/L, below about 30 g/L, orbelow about 40 g/L. Further, microorganisms, such as recombinantmicroorganisms, modified to have certain characteristics to benefit theproduction and recovery of a product alcohol are contemplated herein.For example, a microorganism with a certain level of thermotolerancesuch that elevated fermentation or feed stream temperatures may be moretolerated and therefore provide overall process efficiency. Further,where a fermentative microorganism performs advantageously under certainconditions characteristically, the processes described herein can beutilized to capitalize on such efficiencies. For example, a gas strippermay be used to provide effective air stripping and to provide oxygen formicrooaerobic microorganisms in the fermentation vessel.

Processes described herein can be used in conjunction with a number ofproduct alcohols. Such alcohols include, but are not limited to, loweralkane alcohols such as butanol. In embodiments, the processes describedherein involve production of butanol by a recombinant microorganismcapable of converting a carbon substrate to butanol. Microorganismscapable of converting a carbon substrate to butanol are known in the artand include, but are not limited to, recombinant microorganisms such asthose described in U.S. Patent Application Publication Nos. 2007/0092957and 2009/0305363, in U.S. Provisional Application Ser. Nos. 61/379,546,61/380,563, and in U.S. Nonprovisional application Ser. No. 12/893,089.

With regard to a butanol-producing fermentation, the composition of thestream that leaves the fermentation vessel is typically largely water,and contains the product butanol and CO₂. For certain processesdescribed herein, the vapor stream is contacted with an absorptionliquid in an absorber. In contrast to processes used in the art to treatgas streams that contain acid gasses such as CO₂ and H₂S by absorptioninto specially designed absorption media (Gas Purification, 5th Edition,Arthur Kohl and Richard Neilsen 1997), the methods discovered by theapplicants and provided herein seek to absorb any or all components ofthe vapor stream via the absorption medium. The absorption liquid willabsorb water at a higher temperature than the water would normallycondense. Furthermore, in some embodiments, the product alcohol is alsosoluble in the absorption liquid. While in embodiments of the process,the three components water, butanol, and CO₂ are all absorbed in theabsorption medium, embodiments comprising absorption of any portion ofthe vapor stream to produce a residual vapor stream that is productalcohol rich or CO₂ rich to be further processed still provideadvantages to a vacuum flash fermentation process.

Also, in contrast to processes used in the art to treat gas streams, thecontact with the absorption liquid takes place at a sub-atmosphericpressure close to that of operation of the flash, and in embodimentssubstantially all of the vapor stream is absorbed. The flash andabsorption units can be coupled in such a way as to minimize pressuredrop between the two operations.

To recover the product alcohol, the heat of absorption is removed fromthe absorption liquid, for example, by circulation over a cooler. Insuch an embodiment, the heat can be removed from the circulating fluidusing a cheaper cooling medium than would be required for condensationof the vapor stream without an absorption liquid, the cheaper coolingtypically being via an air cooler or a heat exchanger operating from acooling water circuit or using river water directly. The amount ofabsorption fluid that would need to be re-circulated depends on thetemperature rise that can be allowed over the absorber, which can be anabsorption column. The upper temperature in the absorber is limited byvapor pressures from the solution at the pressure of absorption whilstthe lower temperature is limited by approach to the cold utilitytemperature, normally cooling water.

For processes provided herein, contact of the vapor stream with anabsorption liquid is carried out under a vacuum, and can be carried outat pressures of from about 0.02 to about 0.2 bar. In embodiments, thecontacting can take place at a pressure of less than about 0.2 bar, orless than about 0.1 bar. The contacting can be carried out attemperatures of from about 25° C. to about 60° C. In embodiments, thevaporization step and the contacting step are carried out at the samepressure.

Suitable absorption liquids include those that comprise a water solubleorganic molecule. In embodiments, the water soluble organic molecule hasa boiling point at least 30° C. greater than the boiling point of water.In embodiments, the organic molecule is an amine. In embodiments, theamine is mono ethanolamine (MEA), 2-amino 2-methyl propanol (AMP) ormethyldiethanolamine (MDEA). In embodiments, the molar ratio ofabsorption liquid amine to CO₂ in the vapor stream is at least about1.01 to about 1, i.e., the molar ratio is greater than about 1. Inembodiments, the absorption liquid comprises MEA, AMP, MDEA, or anymixture thereof. The absorption liquid can comprise an ionic solution.In embodiments, the ionic solution comprises a carbonate. Inembodiments, the carbonate is potassium carbonate because of its highersolubility compared to other common alkali metal carbonates. Inembodiments, the amount of carbonate (e.g., potassium carbonate) in theionic solution is an amount sufficient for achieving absorption of atleast a portion (or in embodiments, a substantial portion) of CO₂ fromthe vapor stream. In embodiments, the molar ratio of carbonate (e.g.,potassium carbonate) to CO₂ in the vapor stream is greater than about 1.

In embodiments, the absorption liquid is an ionic liquid. Suitableabsorption liquids for absorption of both water and butanol includethose with the following characteristics: 1) miscible with water andbutanol, 2) normal boiling point of 130° C. or more, or of 150° C. ormore, 3) thermal stability at the boiling point, 4) absence ofprecipitants when exposed to carbon dioxide at a ratio less than 5%weight/weight, or 10% weight/weight, and 5) low corrosively.

While not wishing to be bound by theory, it is believed that absorptionliquids in which at least water will absorb will convey an improvementon the state of the art, provided the temperature of onset of absorptionis greater than the temperature of onset of condensation without thematerial.

In embodiments, the methods provided herein use MEA as the absorptionliquid. MEA solutions in the processes absorb water at a highertemperature than water would condense without the presence of the MEAsolution. Additionally, butanol is soluble in the MEA solution and theMEA solution is also capable of absorbing CO₂.

In embodiments, the methods provided herein use MDEA as the absorptionliquid. MDEA solutions in the processes absorb water at a highertemperature than water would condense without the presence of the MDEAsolution. Additionally, butanol is soluble in the MDEA solution and theMDEA solution is also capable of absorbing CO₂. Whilst other aminescould be used, MDEA also has the advantage that it does not form acarbamide and is therefore readily regenerated.

Suitable absorption liquids include, but are not limited to hygroscopicorganic liquids, high-boiling organic amines, and ionic liquids, as wellas biologically-derived liquids of the above, or mixtures thereof,

Hygroscopic Organic Liquids. Suitable hygroscopic organic liquidscontain components which are soluble in water and water is soluble inthe organic component. These liquids have a higher boiling point thanwater to facilitate absorption of water at a higher temperature than thecondensation point of water. Typically these molecules will require atleast two functional groups on their carbon backbones such as glycolsand diacids. As examples, the absorption liquid can include ethyleneglycol, ethylene glycol monomethyl ether, diethylene glycol, propyleneglycol, dipropylene glycol, polyethylene glycols, polyethylene glycolethers, polypropylene glycol ethers, or a mixture thereof.Biologically-derived 1,3-pronaediol may also be used and may provideoverall carbon-footprint benefit. See e.g., U.S. Pat. No. 7,759,393.,Moreover,

As water is readily soluble in for example, ethylene glycol, hygroscopicorganic liquids provide for absorption from the vapor phase. Further,the solubility of butanol in these liquids (and in particular ethyleneglycol) is better than in water. In some preferred embodiments, thehygroscopic organic liquid may also form an ionic solution. An exampleis potassium carbonate in ethylene glycol solution.

High-boiling Organic Amines. High boiling organic amines, such asalkanolamines, are suitable for use with the processes described herein.Like ethylene glycol, alkanolamines such as MEA and MDEA are misciblewith water and facilitate absorption of water at a high temperature.They are also more miscible with butanol than butanol is with water. Inaddition, they absorb CO₂ absorption through a heat-reversible reaction.

In embodiments, the absorption liquid includes a polyethylenimine orrelated polymeric amino system.

By way of non limitative example, amines that can serve as absorptionliquids for use with the processes described herein can includealiphatic or cycloaliphatic amines having from 4 to 12 carbons,alkanolamines having from 4 to 12 carbons, cyclic amines where 1 or 2nitrogens together with 1 or 2 alkanediyl groups form 5-, 6- or7-membered rings, mixtures of the above solutions, and aqueous solutionsof the above mixtures and solutions.

For example, the absorption liquid can include monoethanolamine (MEA),methylaminopropylamino (MAPA), piperazine, diethanolamine (DEA),triethanolamine (TEA), diethylethanolamine (DEEA), diisopropylamine(DIPA), aminoethoxyethanol (AEE), dimethylaminopropanol (DIMAP) andmethyldiethanolamine (MDEA), any mixture thereof, or any aqueoussolutions thereof.

Ionic Liquids. Ionic liquids are solutions comprising a cation and/or ananion, such as a variety of salts that are in solution at a temperaturebelow 100° C. Examples of suitable ionic liquids include those describedin U.S. Patent Application Publication Nos. 2010/0143993, 2010/0143994,and 2010/0143995, incorporated herein by reference. The presence ofinorganic salts cause a reduction in the vapor pressure of water in thesolution both by dilution and the increased ionization of water.Water-soluble salts are suitable for this process. Suitable forembodiments wherein water is absorbed are solutions comprising saltsthat are highly soluble in water, such as lithium bromide. Generally,the monovalent alkali metals, such as lithium, sodium, potassium will bechosen over other metals because of an increased solubility. The correctchoice of anion can allow CO₂ to also be recovered in the process.Carbonate ion can be employed to absorb CO₂ in the aqueous phase byformation of the bicarbonate ion. Processes using potassium carbonatesolutions are generally referred to as the Benfield Process which, priorto the disclosure herein, has not been used in conjunction with alcoholproduction fermentations to provide a temperature advantage for recoveryof a fermentation product alcohol. In embodiments, a mixed salt solutionsuch as potassium carbonate and a potassium halide salt can be employed.While not wishing to be bound by theory, it is believed that such amixed salt solution will increase the ionic strength of the solution toimprove capture of water without causing precipitation of salts. It isnoted that ionic liquids may absorb ethanol water and/or CO₂ from thevapor phase more efficiently than higher alcohols such as butanol (i.e.,a C3 or higher product alcohol) as well as it can absorb ethanol.

The temperature at the onset of the absorption of the vapor stream intothe absorption liquid phase is greater than the temperature at the onsetof condensation of the vapor stream in the absence of the absorptionliquid phase. The temperature of onset of absorption or condensation canbe assessed by calculation using standard vapor liquid equilibriummethods that are based on experimental data or by direct measurementfrom the process. In embodiments, the temperature at the onset of theabsorption of the vapor stream into the absorption liquid phase isgreater than the temperature at the onset of condensation of the vaporstream in the absence of the absorption liquid phase by at least about2° C.; in embodiments, at least about 3° C.; in embodiments, at leastabout 5° C.; in embodiments, at least about 10° C.; in embodiments, atleast about 15° C.; in embodiments, at least about 20° C.; and inembodiments, at least about 30° C. Equipped with this disclosure, one ofskill in the art will be readily able to use the processes describedherein to minimize the cost of cooling plus the cost of regenerating thesolvent.

It will be appreciated that it is beneficial to absorb as much of thevapor stream as possible into the absorption liquid. In embodiments, atleast about 50% of the vapor stream is captured by the absorptionliquid. In embodiments, at least about 60%, at least about 70%, at leastabout 80%, at least about 90% or at least about 99% of the vapor streamis absorbed into the absorption liquid. In embodiments, the vapor streamcomprises about 50-65% by mass of water, about 30-35% by mass ofbutanol, and about 2-20% by mass CO₂. It will be appreciated thatabsorption, condensation and similar processes are made easier byestablishing a high mass ratio of butanol to carbon dioxide. This ratiois on the order of 1 to 2 parts butanol to 100 parts carbon dioxide forthe fermentation vessel vent. In embodiments, this ratio is increased to1 to 5 parts butanol to 1 part carbon dioxide. In embodiments, thisratio is increased to 5 to 30 parts butanol to 1 part carbon dioxide. Inembodiments, this ratio is increased to 10 to 100 parts butanol to 1part carbon dioxide.

It will be further appreciated that recovery of butanol will be madeeasier to recover by condensation from a stream of a high ratio ofbutanol to water at pressures greater than 0.5 psig. In embodiments,this pressure is increased to 1 to 30 psig. In embodiments, thispressure is increased to 0.9 to 1.2 atmospheres.

In embodiments, the absorption liquid absorbs a substantial portion ofthe CO₂ from the vapor stream. In embodiments, at least about 50%, atleast about 60%, at least about 70%, at least about 80%, at least about90%, at least about 95%, or at least about 99% of the CO₂ is absorbed.For such embodiments, the absorption liquid can be MEA, MDEA, AMP orethylene glycol mixed with potassium carbonate.

Thus, provided herein is a process comprising: partially vaporizing afermentation liquid comprising water and a product alcohol andoptionally CO₂ wherein a fermentation vapor stream is produced; andcontacting the fermentation vapor stream with an absorption liquid phasewherein any portion of the vapor stream is absorbed into the absorptionliquid phase.

In embodiments where product alcohol is absorbed into the absorptionliquid, the product alcohol can be recovered from the absorption liquidsuch that the absorption liquid is concurrently regenerated andrecycled. The recovery and regeneration can be achieved using a processcomprising: pumping an absorption liquid to a higher pressure than thevaporization and absorption took place, such as at a pressure at orabove atmospheric pressure, which would allow venting of residual CO₂from the process; feeding the absorption liquid to a distillation columncomprising a stripping section and optionally a rectification section;distilling the absorption liquid such that a bottoms liquid product anda tops vapor product are produced; and recovering the bottoms productcomprising the absorption liquid phase from the recovery distillationcolumn. The feed to the recovery distillation column can be preheated toreduce the energy input required to the base of the recoverydistillation column using techniques well known to those skilled in theart.

The components removed from the absorption liquid phase and recovered inthe tops vapor product from the recovery distillation can be furtherseparated using conventional methods such as condensation, distillationand decantation, or a combination thereof. Depending on the compositionof the fermentation vapor stream and the absorption liquid employed, inembodiments, the absorption liquid, post vapor stream contact, willcontain a combination of water, product alcohol and, optionally, CO₂ andin certain embodiment all three components.

FIG. 1 depicts an exemplary configuration of equipment, heat exchangers,and product streams for an embodiment of a process 100 described herein.A fermentation to produce butanol (or, in embodiments, other productalcohol(s)) is performed in a fermentation vessel 110, and theconcentration of butanol in fermentation vessel 110 approaches thetolerance level of the microorganism. Fermentation liquid is purged fromfermentation vessel 110 via a stream 124 to a vacuum flash vessel 210 tofacilitate the removal of butanol. In some embodiments, vacuum flashvessel is a flash tank, and the pressure in vessel 210 is maintained atsuch a pressure that in combination with heat that is supplied in theform of partially vaporized water in a stream 216, a sufficient purge ofbutanol is achieved in a vapor stream 212 so as to permit butanol levelsin vessel 110 to be maintained below a preselected threshold given thatthe remaining liquid from vacuum flash vessel 210 is returned tofermentation vessel 110 via a stream 214.

The pressure in vessel 210 can be sufficiently low to achieve thecooling necessary to keep remaining liquid stream 214 and vessel 110 ata temperature acceptable to maintain productivity of the microorganism.The operating pressure of vessel 210 can be between 0.05 and 0.2 bar. Itwill be appreciated that the pressure can be 0.05, 0.1, 0.15 or 0.2 baror less than about 0.2 bar. In embodiments, the ratio of theconcentration of butanol in stream 214 to the concentration of butanolin stream 124 is about 0.9 to about 0.5. It will be appreciated that theratio can be about 0.9, about 0.8, about 0.7, about 0.6, or about 0.5.Vapor stream 212 comprises water, butanol and CO₂. Stream 212 enters anabsorption column 310 where it is contacted with absorption liquidstreams 320 and 324. Absorption liquid streams 320 and 320 comprise anabsorption liquid.

In a non-limiting example, the absorption liquid is an amine, such asMDEA. In a non-limiting example, the absorption fluid is potassiumcarbonate in ethylene glycol. The temperature and absorbentconcentrations of 320 and 324 are maintained at such a level that vaporstream 212 is substantially absorbed. In embodiments, vapor stream 212is substantially absorbed at a temperature of more than about 36° C.while the dew point of stream 212 is less than about 30° C. Residualvapor is removed via a vacuum system via stream 328 and will exit to aplant scrubbing system. There is a liquid recycle stream 322 drawn fromthe bottom of column 310 and cooled in a cooler 301 to produce a stream324 which is circulated back to column 310. In some embodiments, a flowrate of stream 322 will be selected such that the temperature risebetween streams 324 and 322 will be about 3° C. to about 8° C. A liquidpurge is taken from column 310 via a stream 326, which includes theabsorption liquid and CO₂, butanol and water absorbed from vapor stream212. Stream 326 is pumped (pump not shown) to raise its pressure toapproximately atmospheric or higher, and is optionally heated in aheater 311 to produce a stream 330. Heater 311 can conveniently be heatintegrated with a cooler 302 as discussed below.

Stream 330 enters a stripping column 410 which comprises a strippingsection and a rectification section using contacting devices known tothose of skilled in the art. In the stripping section, CO₂, butanol anda substantial fraction of the water is stripped from the absorptionliquid of stream 330. In embodiments, the pressure in stripping column410 is approximately atmospheric and the bottom of stripping column 410is heated to a temperature sufficient to assure that substantially allof the butanol is stripped and the water content of a liquid phasestream 432 including regenerated absorption liquid does not change overtime. In embodiments, the water concentration of liquid phase 432exiting the bottom of column 410 is 10%-40% by mass. Material iscirculated from the bottom of column 410 via a stream 434. Stream 434passes to a heater 413 to produce a stream 436 which is returned tovessel 410. In embodiments, the configuration of heater 413 can be of akettle or thermosyphon readily designed by a person skilled in the art.

Regenerated absorption liquid is pumped (pump not shown) from the bottomof vessel 410 via stream 432, which can first be optionally cooled priorto introduction to absorption column 310. As shown in FIG. 1, inembodiments, regenerated absorption liquid stream 432 is cooled incooler 302 to produce a stream 333. As mentioned above, cooler 302 canconveniently be heat integrated with heater 311 for cooling stream 432.Steam 333 can then optionally be further cooled via cooler 303 toproduce cool absorption liquid stream 320. In embodiments, a side streampurge is taken from the rectification section of stripping column 410via a stream 438. Stream 438 can be substantially free of absorptionliquid and CO₂ and can contain about 1-3% butanol with the remainderbeing water. The water that is contained in stream 330 is substantiallyremoved, via streams 438 and 432, from the downstream part of theprocess which includes column 410 and later-described decanter vessel510 and butanol column 610. Control of stream 438 is such as to achievethe desired water level in stream 432. Stream 438 passes to a heater 411and will be partially vaporized to form stream 216 which is fed to flashvessel 210. As described above, heat from stream 216 can help achievethe balance between vessel 210 and vessel 110 so as to effect asufficient purge of butanol from fermentation liquid feed 124 via vaporstream 212 so as to permit butanol levels in vessel 110 to be maintainedbelow a preselected threshold. In embodiments, heater 411 canconveniently be heat integrated with cooler 404.

Vapor leaves the top of stripping column 410 via a stream 440 and passesto a cooler 404 and separator 505 by which stream 440 is substantiallycondensed and separated from a residual vapor stream 442 to produce aliquid stream 444. Stream 440 can be substantially free of absorptionliquid because of the action of the rectification section in strippingcolumn 410. Residual vapor stream 442 passes to a plant scrubbing system(not shown). Stream 442 includes a major part of the CO₂ fed tostripping column 410, while a major part of the water and butanol ofstream 440 is condensed to form stream 444. Cooler 404 can beconveniently heat integrated with heater 411 and a heater 614 (furtherdiscussed below).

Liquid stream 444 passes to a decanter vessel 510, which also receives astream 652 discussed below. Material in decanter vessel 510 will splitinto an aqueous liquid phase 546 and an organic liquid phase 548. Inembodiments, the aqueous phase or a portion thereof can be returned tothe top of the rectification section of vessel 4 via stream 546. Inembodiments, a portion of either or both of stream 546 and stream 438(discussed above) can be directed to a beer column (not shown).

The organic phase from decanter vessel 510 leaves via stream 548 andpasses to a butanol column 610, which comprises at least a strippingsection. Heat is provided to operate column 610 via a re-circulatingloop of a stream 656 through heater 614 to produce a stream 658, whichis returned to column 610. In embodiments, the configuration of heater614 can be of a kettle or thermosyphon readily designed by a personskilled in the art. If the operating pressure of column 610 issufficiently below that of column 410 and cooler 404, then heater 614can be conveniently heat integrated with cooler 404. The butanol productis taken from the bottom of column 610 via a stream 654. A vaporoverhead stream 650 from column 610 passes to a cooler 405 and iscondensed to produce stream 652. Stream 652 is pumped to decanter vessel510 (pump not shown) where it can be split into aqueous and organicliquid phases.

In embodiments, vacuum flash vessel 210 for achieving vaporization offermentation liquid stream 124 is a multi-stage distillation column 210,instead of a flash tank as described above (which has only one stage).In such embodiments, fermentation liquid feed 124 containing productalcohol is supplied from fermentation vessel 110 at a flow rate tomulti-stage distillation column 210. Fermentation liquid feed 124 isthen partially vaporized in distillation column 210 to produce vaporstream 212 enriched in product alcohol and bottoms stream 214 depletedin product alcohol. In contrast to vaporization carried out in a flashtank as described above, the multi-stage distillation column can beoperated such that the vapor is subjected to more than one stage. Themulti-stage distillation column can have any number of stages from 2 to8 or more. In embodiments, the distillation column is a 6-stage column.As one of skill in the art will appreciate, this leads to a reducedconcentration of product alcohol in bottoms stream 214 (which, in someembodiments, is returned to fermentation vessel 110, as shown in FIG.1). Because product alcohol can be removed from fermentation vessel 110more efficiently using distillation column 210 for the vaporization, theflow rate to the distillation column can be lower than the flow rate toa single-stage vacuum flash tank and still provide for sufficientremoval of product alcohol from fermentation vessel 110. A lower flowrate from fermentation vessel 110 allows for venting of a greaterfraction of CO₂ from the fermentation vessel, thereby lowering the flowrate of vented carbon dioxide by about 2 to about 5 times or more, andtherefore provides for reduced CO₂ in streams subjected to furtherprocessing. Similarly, in embodiments wherein alcohol-depleted bottomsstream 214 or a portion thereof is returned to fermentation vessel 110,more efficient removal of product alcohol from fermentation liquid feedstream 124 allowing for decreased flow rate to multi-stage distillationcolumn 210 likewise allows for a decrease in the flow rate of bottomsstream 214 back to the fermentation vessel. In this configuration, it ispossible to return a bottoms stream of higher temperature to thefermentation vessel without disturbing the temperature of thefermentation beyond acceptable ranges, therefore allowing for themulti-stage distillation column to be operated at higher temperaturethan would otherwise be considered acceptable for a conventionalsingle-stage vacuum flash tank.

Multi-stage distillation column 210 can be a conventional vacuumdistillation column known to those of skill in the art. To achieve theadvantages mentioned above, the multi-stage distillation column isoperated such that the ratio of concentration of product alcohol inbottoms stream 214 is no more than about 90% of the concentration offeed 124, no more than about 50% of the concentration in feed 124, nomore than about 10% of the concentration in feed 124, or, in embodimentsno more than about 1% of the concentration in feed 124. In embodiments,multi-stage distillation column 210 is operated at a temperature rangeof from about 10° C. to about 65° C. and in a pressure range of fromabout 0.2 psia to any pressure under atmospheric pressure. Inembodiments, multi-stage distillation column 210 is operated at atemperature range of from about 25° C. to about 60° C. and in a pressurerange of from about 0.5 to about 3 psia (about 0.2 bars). Inembodiments, the bottom temperature is about 46° C. and the toptemperature is about 36° C.

As with the conventional vacuum flash tank described above, the flowrate to the multi-stage distillation column and the operation thereofare selected such that the titer of product alcohol in fermentationvessel 110 is maintained below a predetermined threshold level selectedin consideration of the tolerance of the microorganism to the productalcohol. Consequently, in embodiments where bottoms stream 214 or aportion thereof is returned to fermentation vessel 110, it isadvantageous to maintain a low concentration of product alcohol in thereturn stream. In embodiments, bottoms stream 214 contains less thanabout 10 g/L, less than about 7 g/L, less than about 5 g/L, less thanabout 2.5 g/L or less than about 1 g/L of the product alcohol.

In embodiments, the presence of carbon dioxide in the fermentationliquid feed to vacuum flash vessel 210 (which can be a vacuum flash tankor a distillation column, as discussed above) can complicate subsequentrecovery of the alcohol, especially recovery by condensation. To reduceor substantially eliminate the amount of carbon dioxide present in thefermentation liquid feed to vessel 210, in embodiments presented herein,carbon dioxide can be pre-flashed from the fermentation liquid at apressure intermediate between atmospheric pressure and the pressure ofthe flash at vessel 210. For example, in any of the processes describedherein, fermentation liquid could be fed to a tank that is maintained ata partial vacuum which is insufficiently low pressure to cause the waterand alcohol to boil but sufficient to pre-flash at least a portion ofthe carbon dioxide from the feed into a resultant vapor. For example,pre-flashing at 0.2 to 0.8 atmospheres pressure can necessitate furthertreatment of the resultant vapor. Such treatment can include compressionand, in some embodiments, cooling of the resultant vapor including thecarbon dioxide (and any associated water and alcohol also present) priorto discharge to the atmosphere. In other embodiments, carbon dioxide canbe partially stripped from the fermentation liquid with a noncondensiblegas such as air or nitrogen. For example, fermentation liquid can becountercurrently contacted with a noncondensible gas in a multistagevapor liquid contractor operating near atmospheric pressure. As anexample, there can be used a three stage countercurrent column whichaccepts sterile compressed air at the bottom in a ratio of 0.2 to 5.0mass units of air per mass units of carbon dioxide in the fermentationliquid, which is fed to the top of the column. The air-stripped carbondioxide, and some quantity of alcohol and water can then be treated, forexample scrubbed, to remove this alcohol before discharge to theatmosphere. Such removal of an amount of carbon dioxide according to theembodiments described here can reduce the complications that carbondioxide can have on the downstream recovery of the alcohol vapor formedin vacuum flash vessel 210.

FIG. 9 illustrates an exemplary process 600 in which at least a portionof carbon dioxide is gas stripped from the fermentation feed upstream offlash vessel 210. Referring to FIG. 9, a stream 125 of mash, yeast andnutrients is introduced into fermentation vessel 110. A stream 122including carbon dioxide is vented from fermentation vessel 110 to awater scrubber system (not shown). Stream 124 of fermentation liquid isheated in a heater 111 and introduced via a pump (not shown) into amultistage, countercurrent gas stripper 205. Stream 124 is contactedwith a stream 220 of noncondensible gas, preferably an inert gas. Insome embodiments, gas stream 220 is air or nitrogen. It should beapparent to one skilled in the art that by varying the number of stagesin stripper 205 and the mass flow ratio of stripping gas 220 tofermentation liquid 124, it is possible to remove at least about 50% ofthe carbon dioxide in the fermentation liquid in some embodiments, andin other embodiments, at least about 55%, about 60%, about 65%, about70%, about 75%, or about 80% of the carbon dioxide in the fermentationliquid. A stream 222 including stripping gas 220 and stripped carbondioxide is vented from gas stripper 205. Stream 222 can be furthertreated, for example, by conveying stream 22 to a water scrubber system(not shown).

A stream 124′ of carbon dioxide-depleted fermentation liquid is passedthrough a valve 117 into a multi-compartment vessel 325, which includesvacuum flash vessel 210 and absorption column 310. In the embodiment ofFIG. 9, flash vessel 210 is a vacuum flash tank that is a compartment ofmulti-compartment vessel 325. Vapor, rich in product alcohol, generatedin the flash tank passes into a second compartment of multi-compartmentvessel 325 and is exposed to cool absorbent liquid stream 324′ whichcauses substantial absorption of the vapor. Residual, unabsorbed vaporand inert gases are vented from multi-compartment vessel 325 via stream328, which can then be conveyed through a compressor train (not shown inFIG. 9) in which vapor stream 328 passed through compressors withintercoolers and exhausted through a water scrubber system. For example,this compressor train can be similar to that shown and described belowin Example 9 with reference to FIG. 8A. Liquid recycle stream 322 ofabsorption liquid is drawn from multi-compartment vessel 325, circulatedat high rate through cooler 301 to remove the heat of absorption, andreturned to multi-compartment vessel 325 as part of cool absorbentliquid stream 324′. A stream 323 of rich absorbent is drawn from thecirculation loop of recycle stream 322 and regenerated via aregeneration process. Regenerated absorption liquid is returned viastream 432 to the circulation loop, cooled through cooler 301, andreturned to multi-compartment vessel 325 as part of cool absorbentliquid stream 324′. The regeneration process (not shown in FIG. 9) canbe similar that that shown and described below in Example 8 withreference to FIG. 7A.

Fermentation liquid 214, partially depleted in alcohol, is pumped fromthe vacuum flash tank of multi-compartment vessel 325. A portion 215 offermentation liquid 214 can be advanced to additional product alcoholrecovery systems for recovery of product alcohol, water andnonfermentables, and the remainder 214′ of fermentation liquid 214 canbe returned to fermentation vessel to further ferment the sugars thereinfor alcohol production.

It should be apparent to one skilled in the art that a vacuum column canbe substituted for the vacuum flash tank of multi-compartment vessel 325in the embodiment of FIG. 9, without departing from the scope of thepresent invention. Also, it should be apparent that flash vessel 210 andabsorption column 310 can be separate vessels connected by conduits,similar to process 100 of FIG. 1, rather being incorporated inmulti-compartment vessel 325. Likewise, in embodiments, any of theprocesses provided herein, including process 100 of FIG. 1, can bealternatively configured such that flash vessel 210 and absorptioncolumn 310 are incorporated in the same vessel such as themulti-compartment vessel 325 described above.

Also, any of the processes provided herein can be operated inconjunction with other vaporization processes, such as those describedin PCT International Publication No. WO2010/151832 A1.

Any of the processes provided herein can be operated and initiated atany time during a fermentation, and can be used to remove butanol orother product alcohol from a fermentation. In an embodiment, a processis initiated concurrently with initiation of a fermentation. In otherembodiments, a process is initiated when the titer of product alcohol inthe fermentation vessel is at least about 8 g/L, at least about 10 g/L,at least about 15 g/L, at least about 20 g/L, at least about 25 g/L, orat least about 30 g/L. In embodiments, processes described herein arerepeated throughout the course of the fermentation. In embodiments,processes described herein are repeated such that the titer of productalcohol in the fermentation vessel is maintained at less than apreselected threshold.

EXAMPLES

Examples 1-4 were designed to determine the ability of certainabsorption fluids to substantially reduce the volatility of carbondioxide, isobutanol and water. The selected absorption fluids weremonoethanolamine, methyl diethanol amine, and a mixture containingethylene glycol and potassium carbonate. The reagents for theseexperiments are provided in Table 1. Example 5 is a comparative examplewithout the absorption fluid.

A method known as the PTx method was used. Use of the PTx method isdescribed in “Phase Equilibrium in Process Design,” Wiley-IntersciencePublisher, 1970, written by Harold R. Null, pages 124 through 126,hereby incorporated by reference. In the PTx method, the total absolutepressure in a cell of known volume is measured at a constant temperaturefor various known loading compositions.

TABLE 1 Reagents page Chemical name CAS # Purity Supplier Cat # (Aldrich2009-2010) Methyl Diethanol Amine 105-59-9 >99% Aldrich 471828 1837(MDEA ) 2-Methyl-1-propanol 78-83-1 99.50%   Aldrich   53132-1 L 1908(I-BuOH) Potassium carbonate 584-08-7 >99.0%   Aldrich 209619-100 g 2250(K₂CO₃) Ethylene Glycol 107-21-1 >99% Aldrich 102466-500 mL 1289Monoethanolamine 141-43-5 >99% Aldrich 398136-500 mL 1246

Carbon dioxide for examples 1-5 was Praxair product CD 4.0 IS-T with aspecification of 99.99% carbon dioxide in the liquid phase (GTS/Welco,Allentown, Pa.).

Deionized water used in these experiments was from a stock supply. Theconductivity of the deionized water was not believed to be relevant tothe examples.

A schematic diagram of a static cell PTx apparatus 200 is shown in FIG.2. The 72.73 cm³ flanged sapphire static cell 700 was immersed in astirred 701, electrically heated Syltherm-800® constant temperature bath702 with a RTD 703, an electricity supply 704, a heater 705 and anEurotherm 2604 temperature controller 706, which controlled temperatureto ±0.01° C. The static cell contained a magnetically driven mixer 710.

This mixer 710 included a 6-bladed Rhuston turbine constructed ofHastelloy C. Gas was entrained through a center whole of the magnet, viaa hollowed carbon bushing, to the hollow shaft. Circulation of gas downthe shaft to two right angle holes, from the vapor space into theturbine was provided to accelerate attainment of an equilibrium betweenthe liquid and gas.

This static cell was leak proof. A port 715 was connected through avalve 716 to a vacuum pump 717 (Gardner Denver Thomas, Inc., WelchVacuum Technology, Niles, Ill.; model 1376N); a port 725 was connectedto an accurate pressure transducer 726 (Druck model # PDCR330; KellerAmerica, Inc., Newport News, Va.); and a port 730 was connected to afeed pump 731 for carbon dioxide. The CO₂ feed pump 731 (Model 87-6-5;High Pressure Equipment Company, Erie Pa.) was sufficiently accurate tosupply a volume known to ±0.001 cm³ at the specified pressure. Pressurein the CO₂ feed pump 731 was measured with a pressure transducer 732(Paro Scientific, Inc. Model 740; Redmond, Wash.). The CO₂ feed pump 731was also in a temperature controlled water bath 733 and could beisolated from the static cell with a valve 734. All compositions arespecified on a component to total weight basis unless otherwise noted.

Example 1 Absorption Liquid MEA

The pressure composition relationship at a known temperature wasmeasured with the described apparatus 200 as follows:

51.967 grams of a mixture of 6.99% isobutanol, 20.01% deionized waterand 72.99% MEA were charged to static cell 700 and magnetically drivenmixer 720 was started. The cell operating temperature was 44.42° C. andthe liquid charge was 51.967 grams. The liquid mixture was degassedslowly by opening valve 716 connected to vacuum pump 717 until the cellpressure did not drop further. Valve 716 was then closed. The degasprocedure was repeated until the cell pressure did not change with timewhen valve 716 to vacuum pump 717 was closed. The absence of leaks wasverified by observing constant, below atmospheric pressure, in staticcell 700 for at least 10 minutes. Cell 700 was heated to a targetedtemperature with bath 702.

A measured volume of carbon dioxide at known pressure and temperaturewas introduced to cell 700 and the cell contents were agitated until thecell pressure remained constant. This cell pressure was noted.Additional carbon dioxide of known volume was added and a constant cellpressure was again noted. This step was repeated until a targetedquantity of carbon dioxide had been added. For the purpose of dataanalysis, the volume of carbon dioxide at known temperature and pressurewas converted to mass using the reference, NIST 14, Thermodynamics andTransport Properties of Fluids, NIST Standard Reference Database 14,Version 4. Results are given in Table 2.

TABLE 2 Effect of MEA on vapor pressure Grams of CO₂ added to cell Vaporpressure in cell - psia 0 0.676 0.4912 0.735 0.9908 0.778 1.4971 0.8261.9656 0.871 2.4939 0.922 3.1277 0.977 3.7217 1.024 4.3925 1.083 5.02841.137

Example 2 Absorption Liquid MEA

The procedures of Example 1 were repeated except the cell operatingtemperature was 44.46° C., the liquid composition was 7.24% Isobutanol,20.57% water, 72.2% Monoethanolamine and the liquid charge was 49.925grams. Results are given in Table 3.

TABLE 3 Effect of MEA on vapor pressure Grams of CO2 added to cell Vaporpressure in cell - psia 0 0.684 0.0739 0.694 0.1577 0.705 0.2798 0.7160.4121 0.724 0.5362 0.734 0.6657 0.742 0.8186 0.752 0.9679 0.761 1.15210.772

Example 3 Absorption Liquid MDEA

The procedures of Example 1 were repeated except the cell operatingtemperature was 44.45° C., the liquid composition was 4.99% Isobutanol,12.01% water, and 83% methyldiethanolamine, and the liquid charge was52.087 grams. Results are given in Table 4.

TABLE 4 Effect of MDEA on vapor pressure Grams of CO2 added to cellVapor pressure in cell - psia 0 0.654 0.0833 0.990 0.1678 1.5 0.30012.428 0.3966 3.153 0.5009 3.97 0.6058 4.812 0.7058 5.643 0.8164 6.5790.9220 7.501

Example 4 Ethylene glycol and potassium carbonate mixture as absorptionliquid

The procedures of Example 1 were repeated except the cell operatingtemperature was 44.52° C., the liquid composition was 6.86% Isobutanol,18.1% water, 9.04% potassium carbonate, and 66.01% ethylene glycol, andthe liquid charge was 56.297 grams

TABLE 5 Effect of ethylene glycol and potassium carbonate mixture onvapor pressure Grams of CO2 added to cell Vapor pressure in cell - psia0 0.886 0.08182 0.892 0.16689 0.898 0.30605 0.913 0.55314 0.953 0.800331.030 1.01325 1.163 1.39296 5.888 1.43120 10.145 1.46580 14.544

Comparative Example 5 Absence of Absorption Liquid

A control experiment was also performed in which CO₂ was added intodeionized water using the same cell. The procedures of Example 1 wererepeated except the cell operating temperature was 49.4° C., the liquidcomposition was 100% deionized water, and the liquid charge was 53.919grams.

TABLE 6 Vapor pressure in the absence of absorption liquid Grams of CO2added to cell Vapor pressure in cell - psia 0 1.74 0.01689 5.00 0.1282326.22 0.22952 45.71 0.33327 65.80 0.43932 86.38 0.53909 105.85 0.64063125.77 0.74679 146.77 0.84640 166.51 0.97062 191.26

The vapor pressure of the absorbent solutions used in Examples 1-4 wereless than the vapor pressure of water alone from Example 5. Addition ofeven small amounts of carbon dioxide to water in the absence ofabsorption liquid, for example 0.01223 grams in 53.919 grams of water,resulted in a substantial increase in the static cell pressure as can beseen in Example 5. Thus, an absorber containing water only, operating atnear 45° C. and less than 2 psia, would condense only a small amount ofcarbon dioxide per unit of water absorption liquid. Some combination ofrefrigerated condensation and a compressor would be required to purgecarbon dioxide from a vacuum flash with only water as an absorptionliquid. An absorber containing ethylene glycol and potassium carbonate,or methyl diethanolamine absorption liquids, at concentrations above 70%would condense more carbon dioxide per unit of absorption liquid thanthe water would at about 45° C. and 2 psia. An absorbent containingmonoethanolamine at a concentration of 70% to 75% would condense evenmore carbon dioxide per unit of scrubbing solution at near 45° C. and 2psia and would require less absorbent per unit of carbon dioxide thanthe other Examples.

Example 6 Absorption and desorption of CO₂: Absorption Liquid MEA

The purpose of this example was to demonstrate carbon dioxide absorptionand then desorption in one of the absorbent solutions, monoethanolamine.

The example was developed using a 1.8L HC60 Mettler RC1 agitated andjacketed calorimeter (Mettler-Toledo Mid Temp, Mettler-Toledo Inc.,Columbus, Ohio) outfitted with a Mettler-Toledo REACT IR model 1000In-Line FTIR using a DiComp, Diamond ATR Probe (Mettler-Toledo). TheDiamond ATR probe was inserted into the RC1 reactor and sealed with aSwagelok fitting to form a pressure tight seal.

The pressure in the calorimeter was measured and recorded by anintegrated Dynisco pressure transducer and RC press data recorder andcontrol system. The weight of the CO₂ cylinder, the reactor contenttemperature, the jacket temperature and the reactor pressures werelikewise measured by components of the RC1 and recorded by the RC1software. The weight of the CO₂ was determined to plus or minus 0.5grams by displacement from a 2A cylinder.

Materials used in the calibration and absorption/desorption experimentdescribed below were monoethanolamine, CAS141-43-5 (catalog no. 398136,purity >99%;Sigma-Aldrich Corp., St. Louis, Mo.); 2-methylpropan-1-ol,CAS No 78-83-1 (Sigma-Aldrich catalog no. 53132-1L of 99.50% purity);and CO₂, 99.8% purity (Airgas East, Salem, N.H.; specification CGA G-6.2Grade H).

Calibrating the FTIR

750.0 g of a solution containing 547.5 g of monoethanolamine, 52.5 g of2-methylpropan-1-ol and 150.0 g of deionized water were added to the RC1calorimeter and heated to 45° C. while agitating at 600 rpm. Thereaction solution was purged with 99.9999% pure nitrogen gas subsurfacethrough a dip tube for 2 hours at a rate of 200 sccm. Nitrogen flow wasstopped and the vessel was then pumped down to a pressure of 0.05 barusing a Welch model 1402 vacuum pump (Gardner Denver Thomas, Inc., WelchVacuum Technology, Niles, Ill.). The degassed fluid in the evacuated andsealed reactor was then exposed to CO₂ at 0.10 bar and 45° C. The CO₂was introduced into the reactor beneath the surface using a ⅛th inchdiameter stainless steel dip tube. The CO₂ was added in 5 g aliquotsuntil 35 g of CO₂ were absorbed. The FTIR spectra were allowed to lineout before additional CO₂ was added at each 5 g increment.

Mid-IR spectra were collected every 2 minutes during the experiments.The absorption of CO₂ into monoethanolamine forms a bicarbonate complexwhich has numerous IR absorbances (see FIG. 3). A band near 1309 cm-1was selected to follow the course of this experiment. A univariateapproach was used to follow the 1309 cm⁻¹ peak with baselines drawnbetween 1341 cm⁻¹ and 1264 cm⁻¹. Absorbances to the two point baselinewere used to create both the bicarbonate calibration plot and thetemperature dependence plot. The CO₂ absorbed vs. peak height at 1309cm⁻¹ is shown in FIG. 4.

The solution with the absorbed CO₂ was heated in a sealed vessel and thepeak height monitored throughout. A temperature vs. peak heightcalibration was generated and is shown in FIG. 5.

After the above calibration, an experiment was conducted to demonstrateabsorption and desorption. 750.0 g of a solution containing 547.5 g ofmonoethanolamine, 52.5 g of 2-methylpropan-1-ol and 150.0 g of deionizedwater were added to the RC1 calorimeter at 45° C. while agitating at 800rpm. The reaction solution was purged with 99.9999% pure nitrogen gassubsurface through a ¼ inch outside diameter, 0.18 ID dip tube for 2hours at a rate of 200 sccm. The vessel was then pumped down to apressure of 0.05 bar using a Welch model 1402 vacuum pump. The degassedfluid was exposed to carbon dioxide at 45° C. The CO₂ was introducedinto the reactor beneath the surface using the ¼ inch outside diameterstainless steel dip tube. The CO₂ was taken up at a nearly constant rateof 6 g/min for nearly 6 minutes until a total of approximately 35 g ofCO₂ was taken up into the reactor. The freeboard in the reactor wasestimated to be about 0.75 liters and so the amount of CO₂ in the vaporspace under these conditions was calculated to be no more than 0.1 g sothat approximately 34.9 g of the 35 g was absorbed into the liquidsolution. The pressure of the reactor was 70 mmHg after the CO₂ wasadded.

The reaction mass was heated to 150° C. at 1° C./min. As the temperaturereached 118° C. the pressure was approximately 1.1 bar. A vent line wasopened and vapor released from the reaction vessel into a verticallymounted condenser cooled with brine at −15° C. The bottom of condensercontacted a reparatory funnel, the bottom outlet of which was openedback to the vessel so as to maintain a constant temperature once thefinal desired reaction temperature was achieved by adjusting the boilingpoint of the solution in the reactor. In this way CO₂ liberated from themonoethanolamine solution was vented from the process while thecondensed liquids were returned. The vent line from the top of thevertically mounted condenser was attached to a bubbler and the formationof bubbles in the bubbler was an indication that CO₂ was being liberatedfrom the reaction vessel. In addition, the in-line FTIR monitored the1309 cm⁻¹ wavenumber peak indicative of the formation of a bicarbonatespecies or complex owing to the reaction of CO₂ and monoethanolamine.The FTIR peak profile indicated complete desorption of the CO₂ from themonoethanolamine peak in about 2.5 hours with over 60% of the desorbedCO₂ regenerated in about ½ hour. After 2.5 hours the 1309 cm⁻¹ peakreturned to its original base line value indicating all of the CO₂ haddesorbed from the monoethanolamine solution. The bubbler also showed nosigns of gas evolution after 2.5 hours.

This example demonstrates that an absorbent solution can be utilized toabsorb carbon dioxide and then regenerated.

Example 7 ASPEN Model: Absorption Liquid Comprising Ethylene Glycol andPotassium Carbonate

Processes described herein can be demonstrated using a computationalmodel of the process. As described in U.S. Pat. No. 7,666,282, processmodeling is an established methodology used by engineers to simulatecomplex chemical processes (and is incorporated herein by reference).The commercial modeling software Aspen Plus® (Aspentech, Burlington,Mass. 01803) was used in conjunction with physical property databases,such as DIPPR, available from the American Institute of ChemicalEngineers, Inc., of New York, N.Y., to develop an ASPEN model of anintegrated butanol fermentation, purification and water managementprocess.

Model inputs are defined in Table 7. A subset of this model illustratingthe invention is best understood by reference to FIG. 6A whichillustrates a flow diagram of a model process 300. Streams and outputsresulting from process 300 described are given in Tables 8A and 8Bprovided as FIGS. 6B and 6C, respectively. Batch fermentation wasmodeled as a steady state, continuous process using average flow rates.

With reference to FIG. 6A, mash stream 23MASH (123), and biocatalyststream YEAST (121) are introduced to fermentation vessel 110. A vaporstream 112VAP (122), containing carbon dioxide, water and butanol, isvented from the fermentation vessel 110 and directed to a butanolrecovery scrubber (not shown). Beer stream 114BEER (114), heated to31.4° C., is passed through a throttling valve 117, and is admitted intovacuum flash vessel 210 (which is a flash tank in this Example) asstream113BEER (124). Flash tank 210 is at 0.1 bar which results in aportion of the beer flashing and a drop in temperature to 28° C. Theflow rate and temperature of stream 113BEER (124) are selected to assurethat the concentration of butanol in fermentation vessel 110 did notexceed 0.025 weight fraction. In this example, the ratio of butanol in aflashed beer stream 115BEER (214) compared to stream 113 BEER (124) is0.85.

Flashed beer stream 115BEER (214) is split into (i) a stream 24BEER(119), which simulates an average flow rate of a purge stream ofnonfermentables and byproducts to additional butanol recovery systems(not shown) for butanol recovery, and (ii) a recycle stream 116REC (116)of yeast and unfermented sugars that is returned back to fermentationvessel 110.

A Stream 67VENT (212), which is vapor from flash tank 210 enriched to31.8 weight percent butanol and with a dewpoint of 28° C., is directedto vacuum absorption column 310 in which nearly all vapors are absorbedwhile operating with a bottoms temperature of 41.2° C. A stream VENT(328) including noncondensibles, and having near zero mass flow rate (inpart representing air leaks into the vacuum equipment), is compressedand discharged to atmosphere through a water scrubber (not shown).

Vacuum absorption column 310 is supplied with two flows of absorbent,absorption liquid streams RICH1B (324) and LEAN (320). In this Example,the absorbent is ethylene glycol containing potassium carbonate andbicarbonate. Stream RICH1B (324) is absorbent re-circulated from thebottom of absorption column 310 after sufficient cooling to remove mostor all of the heat of absorption. Stream LEAN (320) is absorbentreturned from the regeneration process, described below, in sufficientquantity for assuring nearly complete absorption of carbon dioxide,butanol and water. The combined bottoms stream RICH (322′) is divided tosupply stream RICH1B (324) and a stream RICH3 (323), which is dilutedabsorbent that is heated and directed to an absorbent regenerationcolumn (serving as stripping column 410).

Regeneration column 410 is supplied heat at the base by indirectexchange with steam in sufficient quantity to vaporize almost all carbondioxide and butanol, as well as sufficient water, to maintain a steadystate composition. A column bottoms stream LEANT (432) is cooled,including in part by heat rejection to stream RICH3 (323) via a heatintegration, and returned to absorption column 310 as stream LEAN (320).

A stream VAPOR (440) exits regeneration column 410 at one atmosphere andis partially condensed and separated (at vapor-liquid separator 505) toproduce a stream COLVENT (442), which is a carbon dioxide purge that isdischarged through a water scrubber (not shown). Condensate streamCONDENSE (444) is pumped (pump not shown) to condensate decanter vessel510, combined with additional streams not described herein, anddecanted. Decanter 510 generates an organic upper layer BUOH (548) whichis sent to a butanol column (not shown) for purification and,ultimately, commercial sales. A lower aqueous layer AQUEOUS (546) isreturned as reflux to regeneration column 410. A liquid phase side drawis taken from regeneration column 410 between the reflux addition pointand the feed addition point. This side draw stream WATEROUT (450) ispumped to the beer column (not shown) for further recovery of butanol.

TABLE 7 Model Inputs for Example 7 Input Value Units Production 50 MMgal per year Backset 15 % Corn Feed Water Content 15 % Corn Composition(dry) STARCH 70 % C5POLY 5.2 % C6POLY 3 % PROTEIN 9.8 % OIL 4 % NFDS 8 %Waste from Milling 0.3 % Misc Feeds to Mash CIP 2256 kg/hr Enzyme 31.47kg/hr CA 53.6 kg/hr Ammonia 89.8 kg/hr Mash Cooking inlet mashtemperature 190 deg F. intermediate mash temperature approach 18 deg F.to maximum temp Maximum mash temperature 230 deg F. Saccharificationenzyme feed 45.6 kg/hr acid feed 21.1 kg/hr Starch Conversion 99 %Saccharifier Temp 140 deg F. Saccharifier Pres 40 psia Initial Cooldownapproach to 18 deg F. fermentation vessel temperature FermentationVessel yeast feed 8.5 kg/hr inlet temperature 90 deg F. GlucoseConversion 100 % NFDS Conversion Fermentation vessel Temp 90 deg F.Fermentation vessel Pres 16 psia BuOH Titer 25 g/L Flash tank pressure0.7 psia Flash tank liquid recirculation 5061 t/hr CO2 Degasser Degasserpressure 16 psia Degasser condenser temperature 100 deg F. dT betweendegas temp and Beer Col 10 deg C. bottoms cooler exit Beer Column # ofstages 12 column pressures Top 20 psia Bottom 21.5 psia feed stagelocations degassed liquid stage 4 Condensate stage 1 Aqueous refluxstage 1 Butanol mass recovery 99.65 % BuOH Column # of stages 10 columnpressures Top 14.5 psia Bottom 15.2 psia feed stage locations OrganicReflux/Feed Stage 1 Water in Bottom Product 0.01 % BuOH Product Coolerexit temp 104 deg F. exit pres 18.5 psia Scrubber # of stages 7 Pressure15 psia Centrifuge solids/total flow in centrifuge tails 0.287Distiller's Dried Grains with Solubles (DDGS) dryer water concentrationin DDGS product 9 % Evaporators water concentration exit 4^(th)evaporator 60 % 1st evaporator pressure 5.37 psia 2nd evaporatortemperature 63.7 deg C. 3rd evaporator temperature 53.2 deg C.

This Example demonstrates that the absorption temperature is 13° C.higher than the dew point of the vapor stream. Comparing stream 67VENT(212) to stream VENT (328) shows that more than 99% of the vapor streamincluding carbon dioxide is absorbed into the absorption. Furthermore,the Example demonstrates that the absorption liquid can be regeneratedusing processes described herein.

Example 8 ASPEN Model: Vaporization in Multi-Stage Distillation Columnand Absorption Liquid Comprising Ethylene Glycol

An ASPEN model of an integrated butanol fermentation, purification andwater management process was developed. The model inputs are given inTable 9. The model is described with reference to FIG. 7A, whichillustrates a flow diagram of a model process 400. Streams and outputsresulting from process 400 described are given in Tables 10A and 10Bprovided as FIGS. 7B and 7C, respectively. Batch fermentation is modeledin this example as a steady state, continuous process using average flowrates.

With reference to FIG. 7A, mash stream 23MASH (123), and biocatalyststream YEAST (121) are introduced to fermentation vessel 110. A vaporstream 68CO2 (122′), containing carbon dioxide, water and butanol, isvented from fermentation vessel 110 and directed to a butanol recoveryscrubber (not shown). Beer containing 25 grams per liter butanol ispassed through an atmospheric disengagement tank 112 in which vaporsfrom the beer are vented via a stream 68CO2 (122′), which is a streamcombining the vented vapors from fermentation vessel 110 anddisengagement tank 112. The circulated beer is then heated to formstream 26BEER (124), which is introduced into a vacuum flash multi-stagedistillation column 215 (corresponding to vacuum flash vessel 210 of theprocess of FIG. 1). The pressure at the top of column 215 is at 0.07atmospheres, and the butanol concentration in the gas stream is 34.5% bymass. Column 215 is indirectly heated. The number of stages of column215, the heat input to column 215 and the flow rate of stream 26BEER(124) are selected to assure that the concentration of butanol infermentation vessel 110 does not exceed the preselected threshold 0.025weight fraction. Bottoms from vacuum flash column 215 containing 0.3grams per liter butanol is split into (i) a stream 28RCY (128) that isreturned to fermentation vessel 110 to ferment additional sugar tobutanol, and (ii) a stream 29BEER (129) that is directed to a waterrecycle and Distiller's Dried Grains with Solubles (DDGS) productionprocess (not shown). With the methods described herein, compounds thatmay be contaminating to DDGS are isolated from such co-product streamsas opposed to other product removal processes, and therefore may provideadditional benefit to fermentations comprising the product recoverymethods described herein.

A vapor stream 30BOV (212) enriched to 34.5 weight percent butanol isdirected from flash column 215 to vacuum absorption column 310. Inabsorption column 310, approximately 67% of the water plus butanol isabsorbed from vapor stream 30BOV (212), but almost none of the carbondioxide is absorbed. A vapor stream 328 from absorption column 310 iscooled, and a condensate stream 32COND (844 a) is separated (atvapor-liquid separator 805) from residual vapors. From separator 805, aresidual vapor stream 34VAP (342) is compressed, cooled again, and acondensate stream 38COND (844 b) is separated (at vapor-liquid separator806) from residual vapors which form a stream 40VAP (344) that isdirected to a water scrubber (not shown).

Vacuum absorption column 310 is supplied with two flows of absorbent,absorption liquid streams 324 and 320. In this Example, the absorbent isethylene glycol (glycol) without potassium carbonate or other base.Stream 324 is absorption liquid re-circulated from the bottom ofabsorption column 310 after sufficient cooling to remove most or all ofthe heat of absorption. Stream 320 is absorption liquid returned fromthe regeneration process, described below. The combined bottoms stream322′ is divided to supply stream 324 and stream 323. Stream 323 isdiluted absorption liquid (or solution rich with solutes) which isheated and directed to absorption regeneration column 410.

Absorption regeneration column 410 is supplied heat at the base byindirect exchange with steam in sufficient quantity to vaporize butanoland water to maintain a steady state composition. Column bottoms stream432 is cooled, including in part by heat rejection to stream 323 via aheat integration, and returned as stream 320 to absorption column 310.

Vapor stream 440 exits regeneration column 410 at one atmosphere and iscombined with other vapors and partially condensed and separated (atvapor-liquid separator 505) to produce stream COLVENT (442), which is acarbon dioxide purge that is discharged through a water scrubber (notshown). Condensate stream CONDENSE (444) is pumped (pump not shown) tocondensate decanter vessel 510, combined with additional streams notdescribed herein, and decanted. Decanter 510 generates an organic upperlayer 470RG (548) which is sent to a butanol column (not shown) forpurification and, ultimately, commercial sales. A lower aqueous layer48AQ (546) is in part returned as reflux (not shown) to flash column 215and in part used as reflux (not shown) for regeneration column 410.

TABLE 9 Model Inputs for Example 8 Input Value Units Production 50 MMgal per year Backset 15 % Corn Feed Water Content 15 % Corn Composition(dry) STARCH 70 % C5POLY 5.2 % C6POLY 3 % PROTEIN 9.8 % OIL 4 % NFDS 8 %Waste from Milling 0.3 % Misc Feeds to Mash CIP 2256 kg/hr Enzyme 31.47kg/hr CA 53.6 kg/hr Ammonia 89.8 kg/hr Mash Cooking inlet mashtemperature 190 Deg F. intermediate mash temperature 18 Deg F. approachto maximum temp Maximum mash temperature 230 Deg F. Saccharificationenzyme feed 45.6 kg/hr acid feed 21.1 kg/hr Starch Conversion 99 %Saccharifier Temp 140 Deg F. Saccharifier Pres 40 psia Initial Cooldownapproach to 18 Deg F. fermentation vessel temperature Fermentationvessel yeast feed 8.5 kg/hr inlet temperature 90 Deg F. GlucoseConversion 100 % NFDS Conversion Fermentation vessel Temp 90 Deg F.Fermentation vessel Pres 16 psia BuOH Titer 25 g/L Two StageCompressor/Condenser First stage pressure 4 psia Second stage pressure16 psia Vacuum condenser temperature 30 Deg C. Beer Column # of stages 6column pressures Top 1 psia Top condenser temperature 30 deg C. feedstage locations stream from fermentation vessel Stage 1 aqueous refluxStage 1 Butanol mass recovery 99 % EG Absorber # of stages 5 Top P 0.8psia EG Feed Stage 1 Beer vapor feed Stage 5 BUOH Regeneration Col # ofstages 15 Top P 1 atm Reflux Aqueous phase from decanter stage 1 BottomIBA spec 100 ppm BuOH Column # of stages 8 column pressures Top 20 psiaBottom 22 psia feed stage locations Organic Reflux/Feed Stage 1 BuOH inbottoms 99.55 % BuOH Product Cooler exit temp 104 Deg F. exit pres 18.5psia Scrubber # of stages 6 Pressure 15 psia Centrifuge solids/totalflow in centrifuge tails 0.287 DDGS dryer water concentration in DDGS 9% product Evaporators water concentration exit 4th 45 % evaporator 1stevaporator pressure 20 psia 2nd evaporator temperature 99 Deg C. 3rdevaporator temperature 88 Deg C. 4th evaporator temperature 78 Deg C.

This Example shows that use of a multi-stage distillation column canreduce the amount of carbon dioxide removed with butanol whilemaintaining the butanol concentration at or below a preselectedthreshold of 2.5 mass percent in the fermentation tank. Also, themulti-stage distillation column is operated such that the butanolconcentration in the column feed is more than 80 times greater than thatin the bottoms stream returned to the fermentation vessel. Furthermore,use of an absorption liquid, here, ethylene glycol is used without abase, allows absorption of approximately 65% by mass of thesub-atmospheric vapor at an initial condensation temperature of 40.9°C., which is higher than the initial condensation temperature of thesub-atmospheric vapor stream in the absence of an absorption liquid,that is, 37.7° C.

Example 9 Multi-stage Distillation Column Example—No Absorption step

An ASPEN model of an integrated butanol fermentation, purification andwater management process 500 was developed and is described withreference to FIG. 8A. All flow rates were modeled as time averages eventhough they may be non-continuous. Model inputs are given in Table 11,and results are given in Tables 12A and 12B provided as FIGS. 8B and 8C,respectively.

With reference to FIG. 8A, mash and nutrients stream 23MASH (123), andbiocatalyst YEAST stream (121) are introduced to fermentation vessel110. Vapor stream 68CO2 (122′) containing carbon dioxide, water andbutanol are vented from fermentation vessel 110 and directed to abutanol recovery scrubber (not shown). Beer is circulated from 110fermentation vessel to a vacuum beer column 120 (via atmosphericdisengagement tank 112) at sufficient rates to assure that the butanolconcentration in the beer does not exceed a preselected thresholdtarget, in this case 2.5% by weight. In atmospheric disengagement tank112), vapors from the beer are vented and combined with vapor stream68CO2 (122′). The circulated beer is then heated to form stream 26BEER(124), which is introduced into multistage, sub-atmospheric beer column120. The feed point and the number of stages can be optimized by thosefamiliar with the state of the art of beer column design. In this modelthe number of theoretical stages in beer column 120 is 6 and the feed isto stage #1. Sufficient heat is added at the bottom of beer column 120in the form of low pressure steam to reduce the butanol content of thebeer by more than 98%. In this example the pressure at the top of column120 is 1 psia.

A beer column bottoms stream 27BOT (127) is substantially stripped ofbutanol in beer column 120, and a portion of stream 27BOT (127) (about70%) is returned to fermentation vessel 110 as recycle stream 28RCY(128) for further conversion of carbohydrates to butanol. The remainderof the stripped beer, stream 29BEER (129), is sent to a DDGS system (notshown) of the types known in the art as may be necessary to controlaccumulation of suspended solids and other impurities.

A vapor stream 30BOV (130) from beer column 120, enriched in butanol, iscooled, and a liquid condensate stream 32COND (132) and a vapor stream34VAP (134) are separated in a vacuum vapor-liquid separator 905. Theremaining vapor is conveyed through a compressor train, in which it iscompressed, cooled and separated two times (at respective compressor906, vapor-liquid separator 915, compressor 907, and vapor-liquidseparator 925) to produce additional condensate streams 37COND (137) and43COND (143) from separators 915 and 925. A residual vapor stream 40 VAP(140) from this compressor train is above atmospheric pressure and isrouted to a water scrubber (not shown) before discharge to theatmosphere. Condensate streams 32COND (132), 37COND (137) and 43COND(143) are combined with additional streams not described herein, anddecanted in a decanter 515. A water rich lower phase 508 from decanter515 is returned to beer column 120. An organic rich upper phase 506 fromdecanter 515 is sent to a butanol recovery column (not shown) forpurification and, ultimately, commercial sales.

TABLE 11 Model Inputs for Example 9 Input Value Units Production 50 MMgal per year Backset 15 % Corn Feed Water Content 15 % Corn Composition(dry) STARCH 70 % C5POLY 5.2 % C6POLY 3 % PROTEIN 9.8 % OIL 4 % NFDS 8 %Waste from Milling 0.3 % Misc Feeds to Mash CIP 2256 kg/hr Enzyme 31.47kg/hr CA 53.6 kg/hr Ammonia 89.8 kg/hr Mash Cooking inlet mashtemperature 190 deg F. intermediate mash temperature 18 deg F. approachto maximum temp Maximum mash temperature 230 deg F. Saccharificationenzyme feed 45.6 kg/hr acid feed 21.1 kg/hr Starch Conversion 99 %Saccharifier Temp 140 deg F. Saccharifier Pres 40 psia Initial Cooldownapproach to 18 deg F. fermentation vessel temperature Fermentationvessel yeast feed 8.5 kg/hr inlet temperature 90 deg F. GlucoseConversion 100 % NFDS Conversion Fermentation vessel Temp 90 deg F.Fermentation vessel Pres 16 psia BuOH Titer 25 g/L Two StageCompressor/Condenser First stage pressure 4 psia Second stage pressure16 psia Vacuum condenser temperature 30 deg C. Beer Column # of stages 6column pressures Top 1 psia Top condenser temperature 30 deg C. feedstage locations stream from fermentation vessel stage 1 aqueous refluxstage 1 Butanol mass recovery 99 % BuOH Column # of stages 8 columnpressures Top 20 psia Bottom 22 psia feed stage locations OrganicReflux/Feed Stage 1 BuOH in bottoms 99.55 % BuOH Product Cooler exittemp 104 deg F. exit pres 18.5 psia Scrubber # of stages 6 Pressure 15psia Centrifuge solids/total flow in centrifuge 0.287 tails DDGS dryerwater concentration in DDGS 9 % product Evaporators water concentrationexit 4th 45 % evaporator 1st evaporator pressure 20 psia 2nd evaporatortemperature 99 deg C. 3rd evaporator temperature 88 deg C. 4thevaporator temperature 78 deg C.

This Example demonstrates that efficient stripping of butanol in thebeer column permits a flow rate allowing 20002 kg/h of CO₂ to vent fromfermentation vessel 110 and optional atmospheric flash tank (i.e.,atmospheric disengagement tank 112) compared to only 961 kg/h throughsub-atmospheric beer column 120 and compressor train. Consequently, thecompressor is smaller and will require less energy than if a higherfraction of the CO₂ were vented from sub-atmospheric beer column 120.Also, the multi-stage distillation beer column 120 is operated such thatthe butanol mass in the bottoms stream 127 is about 1% of the butanolmass in the feed stream 124.

Example 10 Air Stripping before Vacuum Flash

An ASPEN model of an integrated butanol fermentation, purification andwater management process 700 was developed and is described withreference to FIG. 10A. All flow rates were modeled as time averages eventhough they may be non-continuous. Model inputs are given in Table 13,and results are given in Tables 13A and 13B provided as FIGS. 10B and10C, respectively.

With reference to FIG. 10A, mash and nutrients stream 125, andbiocatalyst (not shown) are introduced to fermentation vessel 110. Avapor stream 122″ containing carbon dioxide, water and butanol arevented from fermentation vessel 110 and directed to a butanol recoveryscrubber (not shown). Beer is circulated from 110 fermentation vessel. Aportion, 415, is directed to a beer column (not shown) to purgenon-fermentables. A portion, 124, is directed to an air stripper 210 atsufficient rates to assure that the butanol concentration in the beerdoes not exceed a preselected threshold target, in this case 2.5% byweight. Carbon dioxide is stripped from the beer in a three stage columnprovided 2308 kg/h of air. The stripping gas flow rate and the number ofstages can be optimized by those familiar with the stripping columndesign. Sufficient heat is added by heater 360 to maintain thetemperature of flash tank 325 (described below) at 32C. The beer ispassed through throttling valve 117 into the lower compartment of vessel325 where it is allowed to flash at a pressure of 0.05 atm, causing thevaporization of butanol, carbon dioxide and water. These vapors,enriched in butanol, pass into compartment 310′ of vessel 325 were theyare partially condensed at 20 C. Condensate is removed from 310′ andpumped through a cooler 401 and returned by stream 424′ to maintain thecondensation temperature. A portion of the condensate, 323′, is removedfrom the circulation loop and further processed to produce productbutanol and water suitable for recycle in facilities not shown. Theremaining vapor, stream 428 is conveyed through a compressor train, inwhich it is compressed, cooled and separated two times as described inExample 8.

Beer not flashed in the flash tank is pumped (not shown) by stream 414to return nutrients to the fermentation vessel for further fermentation.

TABLE 12 Model Inputs for Example 10 Input Value Units Production 40 MMgal per year Backset 15 % Corn Feed Water Content 15 % Corn Composition(dry) STARCH 70 % C5POLY 5.2 % C6POLY 3 % PROTEIN 9.8 % OIL 4 % NFDS 8 %Waste from Milling 0.3 % Fermentation vessel yeast feed 8.5 kg/hr inlettemperature 90 deg F. Glucose Conversion 100 % NFDS ConversionFermentation vessel Temp 90 deg F. Fermentation vessel Pres 16 psia BuOHTiter 25 g/L Air Stripper Stages 3 Air flow rate 2308 Kg/h Flash TankPressure 0.05 Atm Inlet Temperature 31.8 deg C. Condenser temperature 20deg C.

This Example demonstrates that air stripping of beer after thefermentation vessel and prior to flashing will reduce the CO₂ content inthe vapor from the flash. Consequently, the vapors from the flash may bemore completely condensed at temperatures on the order of 20 C.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the scope of the invention. Thus, thebreadth and scope of the present invention should not be limited by anyof the above-described exemplary embodiments, but should be defined onlyin accordance with the following claims and their equivalents.

All publications, patents and patent applications mentioned in thisspecification are indicative of the level of skill of those skilled inthe art to which this invention pertains, and are herein incorporated byreference to the same extent as if each individual publication, patentor patent application was specifically and individually indicated to beincorporated by reference.

What is claimed is:

1. A method for removing a product alcohol from a fermentation liquid,comprising: (a) at least partially vaporizing a fermentation liquid feedwherein a vapor stream is produced, the fermentation liquid feed and thevapor stream each comprising an amount water, a product alcohol and CO₂;and (b) contacting the vapor stream with an absorption liquid undervacuum conditions wherein at least a portion of the vapor stream isabsorbed into the absorption liquid to form an absorption liquid phase,wherein the portion of the vapor stream that is absorbed includes anamount of each of the water, the product alcohol and the CO₂, andwherein the temperature at the onset of the absorption of the vaporstream into the absorption liquid is greater than the temperature at theonset of condensation of the vapor stream in the absence of theabsorption liquid.
 2. The method of claim 1, wherein the (a) vaporizingcomprises: (i) removing the fermentation liquid feed from a fermentationvessel; (ii) supplying the fermentation liquid feed to a multi-stagedistillation column at a flow rate; (iii) distilling the fermentationliquid feed to produce the vapor stream enriched in the product alcoholand a bottoms stream depleted in the product alcohol, wherein thedistilling occurs under a pressure sufficiently below atmospheric toallow for the vapor stream to be produced at a temperature no greaterthan about 45° C.; and (iv) optionally, returning any portion of thebottoms stream to the fermentation vessel, wherein the concentration ofthe product alcohol in the bottoms stream is not more than about 90% ofthe concentration of the product alcohol in the fermentation liquidfeed.
 3. The method of claim 1, wherein the (a) vaporizing and the (b)contacting are carried out at a pressure of less than about 0.2 bar. 4.The method of claim 1, wherein the (a) vaporizing step and the (b)contacting step are carried out at a pressure of less than about 0.1bar.
 5. The method of claim 1, wherein at least about 90% of the vaporstream is absorbed into the absorption liquid phase.
 6. The method ofclaim 1, wherein the temperature at the onset of the absorption of thevapor stream into the absorption liquid is at least about 10° C. greaterthan the temperature at the onset of condensation of the vapor stream inthe absence of the absorption liquid.
 7. The method of claim 6, whereinthe temperature at the onset of the absorption of the vapor stream intothe absorption liquid phase is at least about 30° C.
 8. The method ofclaim 1, wherein the product alcohol is butanol.
 9. The method of claim8, wherein the product alcohol is isobutanol.
 10. The method of claim 1,wherein the absorption liquid comprises a water soluble organic moleculewith a boiling point at least about 30° C. greater than the boilingpoint of water at atmospheric pressure.
 11. The method of claim 1,wherein the absorption liquid comprises potassium carbonate and ethyleneglycol.
 12. The method of claim 1, wherein the absorption liquidcomprises glycol.
 13. The method of claim 12, wherein the glycolcomprises ethylene glycol, propylene glycol, or a mixture thereof. 14.The method of claim 13, wherein the absorption liquid comprises ethyleneglycol.
 15. The method of claim 10, wherein the organic molecule is anamine.
 16. The method of claim 15, wherein the amine is selected fromthe group consisting of monoethanolamine (MEA), 2-amino 2-methylpropanol (AMP), and methyldiethanolamine (MDEA).
 17. The method of claim1, wherein the absorption liquid comprises MEA, AMP, MDEA, or anymixture thereof.
 18. The method of claim 17, wherein the absorptionliquid comprises MEA.
 19. The method of claim 17, wherein the absorptionliquid comprises AMP.
 20. The method of claim 17, wherein the absorptionliquid comprises MDEA.
 21. The method of claim 17, wherein theabsorption liquid comprises a mixture of at least two of MEA, AMP, andMDEA.
 22. The method of claim 15, wherein the molar ratio of absorptionliquid to CO₂ in the vapor stream is greater than about
 1. 23. Themethod of claim 1, further comprising distilling the absorption liquidphase containing the absorbed vapor stream under conditions sufficientto remove a substantial portion of the water, the product alcohol, andthe CO₂ from the absorption liquid.
 24. The method of claim 1, wherein asubstantial portion of the CO₂ and at least a portion of at least one ofthe product alcohol and the water or both are absorbed into theabsorption liquid.
 25. The method of claim 24, wherein a substantialportion of each of the CO₂, the product alcohol and the water areabsorbed into the absorption liquid.
 26. The method of claim 1, furthercomprising, prior to the (a) vaporizing step, one or both of (i) gasstripping a portion of the CO₂ from the fermentation liquid feed and(ii) vaporizing a portion of the CO₂ from the fermentation liquid feed.27. The method of claim 26, wherein a portion of the CO₂ from thefermentation liquid feed is gas stripped from the fermentation liquidfeed prior to the (a) vaporizing step, where the portion of the CO₂ isgas stripped by countercurrent contact of the fermentation liquid feedwith a noncondensible gas.
 28. A method for removing a product alcoholfrom a fermentation liquid, comprising: (a) at least partiallyvaporizing a fermentation liquid wherein a vapor stream is produced, thefermentation liquid and the vapor stream each comprising an amount ofwater, butanol, and optionally CO₂; and (b) contacting the vapor streamwith an absorption liquid under vacuum conditions wherein at least aportion of the vapor stream is absorbed into the absorption liquid toform an absorption liquid phase, wherein the portion of the vapor streamthat is absorbed includes an amount of each of the water and thebutanol, and optionally CO₂, and wherein the temperature at the onset ofthe absorption of the vapor stream into the absorption liquid is greaterthan the temperature at the onset of condensation of the vapor stream inthe absence of the absorption liquid.
 29. The method of claim 28,wherein the absorption liquid comprises a water soluble organic moleculewith a boiling point at least about 30° C. greater than the boilingpoint of water at atmospheric pressure.
 30. The method of claim 28,wherein the organic molecule is an amine selected from the groupconsisting of monoethanolamine (MEA), 2-amino 2-methyl propanol (AMP),and methyldiethanolamine (MDEA).
 31. The method of claim 28, wherein theabsorption liquid comprises ethylene glycol.
 32. The method of claim 28,wherein the (a) vaporizing comprises: (i) removing the fermentationliquid feed from a fermentation vessel; (ii) supplying the fermentationliquid feed to a multi-stage distillation column at a flow rate; (iii)distilling the fermentation liquid feed to produce the vapor streamenriched in butanol and a bottoms stream depleted in the productalcohol, wherein the distilling occurs under a pressure sufficientlybelow atmospheric to allow for the vapor stream to be produced at atemperature no greater than about 45° C.; and (iv) optionally, returningany portion of the bottoms stream to the fermentation vessel, whereinthe concentration of the product alcohol in the bottoms stream is notmore than about 90% of the concentration of the product alcohol in thefermentation liquid feed.
 33. The method of claim 32, wherein thefermentation liquid comprises CO₂, wherein the (a) vaporizing furthercomprises, prior to the (ii) supplying, one of gas stripping gas aportion of the CO₂ from the fermentation liquid feed and vaporizing aportion of the CO₂ from the fermentation liquid feed.
 34. The method ofclaim 33, wherein the portion of the CO₂ is gas stripped or vaporizedafter the (i) removing step.
 35. A method for maintaining the titer ofproduct alcohol in a fermentation vessel below a preselected threshold,the method comprising: (a) removing from a fermentation vessel afermentation liquid feed stream produced from a fermentation in thefermentation vessel, the fermentation liquid feed stream comprisingproduct alcohol, water, and optionally CO₂; (b) supplying thefermentation liquid feed stream to a single stage flash tank or amulti-stage distillation column; (c) at least partially vaporizing undervacuum conditions the fermentation liquid feed stream in the singlestage flash tank or the multi-stage distillation column to produce avapor stream enriched in product alcohol and a bottoms stream depletedin product alcohol; (d) optionally returning any portion of the bottomsstream to the fermentation vessel; and (e) contacting the vapor streamwith an absorption liquid under vacuum conditions wherein at least aportion of the vapor stream is absorbed into the absorption liquid,wherein the absorption liquid comprises a water soluble organic moleculedifferent from the product alcohol.
 36. The method of claim 35, whereinthe temperature at the onset of the absorption of the vapor stream intothe absorption liquid is greater than the temperature at the onset ofcondensation of the vapor stream in the absence of the absorptionliquid.
 37. The method of claim 36, wherein the concentration of productalcohol in the bottoms stream is less than about 90% of theconcentration of product alcohol in the fermentation liquid feed stream.38. The method of claim 37, wherein the concentration of product alcoholin the bottoms stream is less than about 10% of the concentration ofproduct alcohol in the fermentation liquid feed stream.
 39. The methodof claim 35, wherein the organic molecule is an amine.
 40. The method ofclaim 35, wherein the organic molecule is ethylene glycol.
 41. Themethod of claim 35, wherein the concentration of product alcohol of thebottoms stream is less than about 2.5 g/L.
 42. The method of claim 35,wherein the fermentation liquid feed stream comprises CO₂.
 43. Themethod of claim 35, wherein the method is initiated when the productalcohol in the fermentation vessel reaches about 10 g/L.
 44. The methodof claim 35, wherein the method is initiated concurrently withinitiation of the fermentation producing the fermentation liquid feedstream.
 45. The method of claim 35, further comprising: repeating steps(a)-(d) such that the product alcohol in the fermentation vessel ismaintained at less than about 40 g/L during the fermentation in thefermentation vessel.
 46. A method of recovering a product alcohol froman absorption liquid phase and regenerating the absorption liquid phase,comprising: (a) pumping from an absorber an absorption liquid phasecomprising an absorption liquid, water, product alcohol, and optionallyCO₂, to a higher pressure than a pressure in the absorber; (b)optionally, heating the absorption liquid phase; (c) feeding theabsorption liquid phase to a multi-stage distillation column comprisinga stripping section and optionally a rectification section; (d)operating the distillation column under conditions such that a bottomsproduct comprising the absorption liquid and a vapor phase comprising amixture of water, product alcohol, and optionally CO₂ are produced; (e)recovering the bottoms product comprising the absorption liquid phasefrom the distillation column; and (f) recovering the water, the productalcohol and optionally CO₂ from the vapor phase.
 47. The method of claim46, further comprising: (g) causing to be separated the constituentparts of the vapor phase from (f) by condensation, distillation,decantation, or a combination thereof.
 48. The method of claim 46,further comprising: (g) at least partially condensing the vapor phaseproduced in step (d) to form a two liquid phase mixture; (h) passing theliquid phase mixture to a decanter wherein the liquid phase mixture isseparated into an aqueous phase and an organic phase (i) passing atleast portion of the aqueous phase to the rectification section of thedistillation column of step (c); (j) removing a liquid side stream fromthe rectification section of the distillation column and returning it toa vacuum flash vessel configured to receive a fermentation liquid feedstream comprising product alcohol, water, and optionally CO₂; (k)passing at least a portion of the organic phase to a second distillationcolumn comprising a stripping section; (l) withdrawing a product alcoholfrom a bottom of the second distillation column; (m) withdrawing vaporsfrom a top of the second distillation column; (n) causing the vaporsfrom (m) to be cooled so that the vapors partially condense to form twoliquid phases; and (o) passing the liquid phases from (n) to a decanter.49. The method of claim 1, further comprising substantially reducing theamount of carbon dioxide present in the fermentation liquid feed tovessel 210, by pre-flashing from the fermentation liquid at a pressureintermediate between atmospheric pressure and the pressure of the flashat vessel
 210. 50. The method of claim 1, further comprisingsubstantially reducing the amount of carbon dioxide present in thefermentation liquid feed to vessel 210, by non-condensable gas strippingprior to the flash vessel
 210. 51. The method of claim 1, wherein theproduct alcohol is butanol and a portion of the CO₂ butanol and waterare volatilized prior to beer stripping wherein said partialvolatilization provides improved process efficiency.
 52. The method ofclaim 1, wherein the vapor stream that is partially vaporized and thevapor stream absorbed into the absorption liquid are 1 to 100 parts bymass butanol to one part carbon dioxide.
 53. The method of claim 52,wherein said vapor streams are 10 to 100 parts by mass butanol to onepart carbon dioxide.
 54. The method of claim 46, wherein the pressure ofthe vapor phase comprises 1 to 100 parts by mass butanol to one partcarbon dioxide and the pressure is 1 to 30 psig.
 55. The method of claim54, wherein said pressure is 0.9 to 1.2 atmospheres.
 56. A vapor streamof claim
 52. 57. The isobutanol produced by the method of claim 9.